1. Field of the Invention
The present invention relates, in general, to air conditioning apparatus. In particular, the invention relates to an air conditioning apparatus employing a refrigerant heating device which heats refrigerant in a heating operation.
2. Description of the Related Art
A heat-pump type air conditioning apparatus is well known and is used as a heater in winter season. In a heating operation, an external heat-exchanger of the heat-pump type air conditioning apparatus acts as an evaporator and an internal heat-exchanger acts as a condenser. Refrigerant taken into the compressor absorbs heat from the atmosphere through the evaporator and refrigerant output from the compressor discharges heat through the condenser into a defined space to be heated. The above-described heating cycle is repeatedly carried out to provide heat into the defined space.
In the above-described conventional air conditioning apparatus, a refrigerant collecting operation is generally carried out to collect refrigerant from the heat-exchanger to the compressor when the heating operation is reexecuted. During the refrigerant collecting operation, the above-described heating cycle has not been carried out. Thus, the start of the heating operation is delayed when the heating operation is commanded.
An air conditioning apparatus including a refrigerant heating device is well known. In this type of the air conditioning apparatus, two different external heat-exchangers may be used in one refrigerating circuit. One is an ordinary type of the heat-exchanger which is used in a cooling operation, as a condenser. The other is a heat-exchanger of the refrigerant heating device which is used as an evaporator in a heating operation. When the restart of the heating operation is commanded, the heating operation is immediately carried out without executing the refrigerant collecting operation.
In such a conventional air conditioning apparatus including a refrigerant heating device, the closed heating circuit is maintained by the four-way valve being activated after the heating operation is halted. Thus, escape of refrigerant, so called a hot gas, from the closed heating circuit to the external heat-exchanger which is used in a cooling operation is avoided.
However, owing to the inherency of the mechanical arrangement of the four-way valve, an amount of refrigerant leaking from the high pressure side of the compressor through the four-way valve to the external heat-exchanger acting as a condenser in a cooling operation is increased if a period of time from the halt of the heating operation to restart of the heating operation is extended or the external temperature is excessively low. If the heating operation is restarted without collecting the increased amount of a leaked refrigerant in the heat-exchanger as described above, the shortage of refrigerant occurs in the closed heating circuit, and thus a heating capacity of the air conditioning apparatus is decreased.
On the other hand, the above-described refrigerant collecting operation is carried out for a prescribed period of time (a fixed value) measured by a timer. The refrigerant collecting operation is promoted if the external temperature is high. The suction pressure of the compressor becomes negative, and then an unusual operation, so called a vacuum driving, of the compressor may occur. The compressor is operated in a vacuum condition. Thus, the high compressing pressure section of the compressor is overheated and is damaged if such an unusual operation of the compressor is continued.